Probably OSHA guidelines not keeping up with technology. Technically they're operating machinery on-site. There's probably a line somewhere that states that if you're operating machinery on-site you need to be wearing the appropriate gear.

The concept of driving a vehicle while not being in the area wasn't a possibility they considered while writing the regulations.

And yes, you could say that they should "just use common sense", but that's a fuzzy line. There's often good sounding excuses as to why one should not follow the regulations to the letter "this time". And those are the times bad stuff happens.

But is it be what the truck drivers should be doing?

I mean automating things may sound noble, until it affects your own job.

And wouldn't you be wary if someone came into your office, installed a camera, and told you your job would be fully automated in a few weeks?